In the chemical, food processing and pharmaceutical industries, gas fluidizing conveyors typically are used for conveying powder and fine granular bulk materials. Such conveyors generally consist of a lower trough into which fluidizing gas is introduced, a gas permeable membrane sealed against the upper side of the lower trough and an upper cover to enclose and channel the flowing fluidized material and to prevent the escape of airborne dust into a plant environment except at the end of the conveyor. Typically, such conveyors are installed at a downwardly inclined angle between the inlet and the outlet to facilitate the flow of the fluidized material under the force of gravity. In operation, the fluidized material forms a continuous flowing mass which flows freely to the lower end of the inclined conveyor. The discharge rate and velocity of the material flow of such conveyors may be controlled by varying the angle of incline of the conveyor and by modulating the fluidizing gas flow entering the lower trough and subsequently passing upwardly through the gas permeable membrane. Such conveyors generally are employed beneath silos equipped with vibratory or fluidizing type discharges, but operate substantially independent of the silo discharge system. This type of conveyor does not depend upon silo discharge pressure for its operation and its discharge opening normally is not 100 percent full of material over its opening cross section. Fluidizing conveyors of the type described are limited in application only to materials which are readily fluidizeable and not to more coarse materials which would require large volumes of air or gas for fluidization. Because of such limitations, it is desirable to provide a material handling system including means for pneumatically conveying bulk particulate materials which is capable of conveying particulate materials of a broader range of sizes with the use of less gas as a conveying medium and without the need to incline the conveyor to provide gravity flow.
Accordingly, it is the principal object of the present invention to provide an improved material handling system including means for pneumatically conveying bulk particulate materials of a broader range of sizes than comparable prior art systems, controlling the flow rate of material being conveyed, utilizing less gas as a conveying medium and not requiring any particular orientation of the direction of flow of the material.
The present invention provides an improved system for handling bulk particulate material generally comprising a vessel for holding a supply of such bulk particulate material, a container into which such material is to be transported and a transport line for pneumatically conveying such material from such vessel to the container. The transport line includes a first elongated tube formed of a gas permeable material having an inlet communicating with the vessel; a second elongated tube formed of a gas impervious material encompassing the first tube and spaced therefrom about the periphery of the first tube; a plurality of transversely disposed partitions disposed between the first and second tubes, spaced along the lengths thereof, forming a plurality of chambers encompassing the first tube; each of the chambers having means for selectively introducing a fluidizing gas independently of the other chambers at variable volumes and pressures whereby the volume and pressure of fluidizing gas defused through the first tube may be modulated along the length thereof; and means for injecting a flow inducing gas into the first tube. Preferably, the transport line consists of a plurality of sections which may be joined together in end-to-end relation, in various lengths, orientations and configurations, and further means are provided for injecting a flow enhancing gas at spaced intervals along such transport line.